"Pokemari" is something made up for Pokemon Conquest, but it has a historical basis, though obscure and ultimately not really important.
The Warlord of Chrysalia is Imagawa Yoshimoto, and the real-life Yoshimoto's son Ujizane was apparently a big fan of kemari. Kemari was a ball game where you used your limbs or a weapon or tool of some kind to bounce a ball around as long as possible, and it became really popular among the nobility in feudal Japan to the point of being considered a form of art. Yes, seriously, it was basically hacky sack but treated with respect and prestige.
So Yoshimoto's obsession with Pokemari is taking the real-life historical nobility's obsession with kemari, and pushing it to the most absurd extreme.